Producing complete grammatical utterances is one of our most important skills. In developing individuals, in those with disordered language, and in unimpaired adults, the cognitive and neural mechanisms that underlie the ability to produce full sentences change and learn with ongoing experience. This application describes a series of experiments that are designed to gain key insights into how ongoing experience changes the cognitive and neural mechanisms we use to produce language. The experiments focus on syntactic flexibility, which refers to the fact that given situations can be described with more thn one sentence structure. For example, one can grammatically say either I bought brunch for my mother or I bought my mother brunch. This is an essential aspect of our grammatical knowledge, as it allows speakers to use sentence structures to communicate more efficiently or effectively. The proposed experiments will explore how experience changes speakers' linguistic knowledge as it related to syntactic flexibility across three specific aims. First, when speakers hear new words in sentences (specifically, verbs), what do they learn so that they are later able to use those words in their own sentences? The experiments in this specific aim will determine not only how speakers learn the structures they hear used with new words, but also how speakers generalize their particular experience to be able to produce other related structures that they did not hear used with the new words. Second, depending on what has already been said in a discourse, or what speakers mean to talk about, it is sometimes more appropriate to use one sentence option rather than another. For example, people use sentence options so that things that have already been talked about can be mentioned sooner in their sentences. The experiments in this specific aim will determine how ongoing experience can change our knowledge of the factors that make one sentence option more appropriate to use than another. Third, when people refer back to things that were previously described, their current descriptions tend to be similar to the previous descriptions. This conveys agreement among speakers and makes language use more predictable. In this specific aim, we extend these observations into the domain of syntactic flexibility, and determine how and when speakers refer to particular events using the same sentence options as they previously heard for those events. The proposed research will foster better understanding of the paths by which people's ability to use language are subject to learning and change with experience. This is relevant to critical health processes including typical and disordered first language development, including with conditions such as Specific Language Impairment and autism spectrum disorders, as well as rehabilitation of language ability after brain insult.